Lung contusion is a common injury sustained by victims of motor vehicular accidents and blast trauma. It is also an independent risk factor for the development of ALI, ARDS and ventilator associated pneumonia. It is frequently associated clinically with gastric aspiration at the time of trauma that can further increase the severity of lung injury and the risk of ALI/ARDS based on our preliminary studies in animals. The current proposal studies murine models of both isolated lung contusion and lung contusion with gastric aspiration. Emphasis is on mechanistic understanding of the protective roles of MCP-1and MCP-5 in the pathogenesis of these injuries alone and in combination, including specific effects of this chemokine in facilitating the recruitment and activation of alveolar macrophages and the subsequent phagocytosis of apoptotic neutrophils. The grant has three Specific Aims. Aim 1 investigates lung injury and innate pulmonary inflammation in lung contusion in knockout mice lacking MCP-1, MCP-5 or the receptor protein CCR2, as well as in wild type mice given antibodies against these molecules. These in vivo studies are complemented by added experiments where isolated alveolar macrophages are examined ex vivo for phenotypic parameters, phagocytic potential, and cell-specific inflammatory mediator profile. Additionally, an investigation of origin of cells primarily responsible for the production of MCP-1 in lung contusion through the use of bone marrow-derived chimeras is proposed. In addition, the importance of TLR9 with the intracellular adaptor protein MyD 88 as an intermediate in the recognition of injury and the subsequent activation and elaboration of MCP-1 from alveolar macrophages is investigated. Aim 2 involves analogous studies to those in Aim 1 to define the detailed activities and mechanisms of action of MCP-1 and MCP-5 in the combined injury model of lung contusion with gastric aspiration. The precise mechanisms of activity of chemokines with alveolar macrophage activity and role of TLR9 in the production of MCP-1 or MCP-5 are similar to aim 1. Aim 3 examines the effects of delivering exogenous MCP-1 to the lungs via direct instillation and by electroporation-facilitated gene delivery of DNA plasmids containing MCP-1 to MCP-1 (-/-) and wild type mice following lung contusion and lung contusion with gastric aspiration. These latter studies extend Aim 1 and 2 to further document the functional significance of MCP-1 in lung contusion with and without gastric aspiration, while at the same time investigating the efficacy of potential future therapies based on the pulmonary delivery of this chemokine or related agents.